The present invention relates to compound archery bows, and more particularly to a cam system for a compound bow including an adjustment module.
Conventional compound archery bows include a bowstring and a set of cables, usually an up cable and a down cable, to transfer energy from the limbs and cams or pulleys of the bow to the bowstring, and thus to an arrow shot from the bow. The cables and/or bowstring are strung from a cam or pulley on one limb to a cam or pulley on another limb. The function of the cam system is to provide a mechanical advantage so that energy imparted to the arrow is a multiple of that required of an archer to draw the bow.
Most compound bows are outfitted with either single cam systems or dual cam systems, and are set-up to accommodate the specific draw length of the archer shooting the bow. As used herein, draw length generally refers to the distance, at full draw, between the nocking point of the arrow on the bowstring to the back of the grip on the bow. Regardless of the cam system, most systems include a mechanism that enables an archer to modify draw length of the bow so that it is suitable to their physical stature, to provide a stop location in the draw cycle of the bowstring so that the archer knows when the bow is fully drawn, and/or to provide the archer with a consistent reference associated with their preferred draw stop location.
Single cam systems usually include a single cam on a lower bow limb and a single track pulley on an opposing upper bow limb, with one cable and one bowstring, wrapped around the cam and/or pulley. Depending on the particular design, the cam system can be altered to adjust draw length with one of several constructions.
In one construction, the entire cam can be replaced with another cam having different draw length characteristics. In another construction, the cam can include a replaceable module, which module includes a groove for either the bowstring or the cable, attached to the cam. The module, in this instance, can be replaced with another module having different draw length characteristics. When replacing the module of this construction, extra care must be taken to remove and replace the cable or bowstring relative to the groove in the module. Further, special equipment, such as a bow press, may be required to replace the module of this construction. In addition, the module of this construction is usually joined to the cam with a screw threaded into a threaded hole defined by the cam. This simple screw attachment can sometimes lead to inappropriate registration of the module and the cam if the threads are not perfectly matched, if the threaded hole is not perfectly drilled, or if the screw or hole wear under the force of multiple draw cycles and shooting of the bow over time.
In yet another construction, called a “rotating module” design, a cam module includes a groove that accommodates a cable or a bowstring. The rotating module also includes a pivot point about which it is rotated and subsequently oriented relative to the cam in any one of several positions. The various rotational positions provide different draw length characteristics.
A conventional older cam system employs two cams, two cables, and one bowstring where each cable is connected on one end, by means of a yoke, to the axle of the opposite cam. One or both cams can include a rotating module or a fixed adjustment module, adapted to be rotated or changed out, respectively, to adjust draw length.
Another more recent variant of the dual cam system, often referred to as a “cam and a half,” has one cable connected by a yoke to an axle on which one cam rotates and the other cable connected cam to cam. Still another variant employs a three-track cam design. A newer variation of the dual cam system can employ two-track cams of monolithic design—monolithic in the sense that there is no separate module for draw length adjustment. Draw length adjustment on the above cam variations can be provided by rotating a cam module or by removing and replacing one module with another as noted above.
While most conventional cam systems provide satisfactory performance, they require significant time and effort to adjust the draw length, the draw force curve of the bow and the draw stop. For cam systems that utilize cam module replacement for adjusting draw length, the usual added expense of servicing the bow by an experienced bow technician, or the use of a bow press, can be deterrents in making the draw length desired change. Further, the sometimes inaccurate or imprecise registration between a module and a cam can lead to premature wear on these components, as well as other components of the bow, such as the bowstring and the related axles. Accordingly, there remains room for improvement in cam system design to provide a relatively simple and precise way to adjust draw length, draw stop and the draw force curve of a cam system and an associated archery bow.